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From Mark Thomas <ma...@apache.org>
Subject Re: Change of status code for ClientAbortExceptions - bug?
Date Wed, 07 Jun 2017 08:51:06 GMT
On 06/06/17 23:11, Konstantin Kolinko wrote:
> 2017-06-07 0:10 GMT+03:00 Mark Thomas <markt@apache.org>:
>> On 06/06/17 15:08, Thomas Eliassen wrote:
>>>
>>> Is there some way to avoid having it logged as a 500 in the access log then?
>>
>> At the moment, no. And my preference is to avoid creating new
>> configuration options unless we have to.
>>
>>> ClientAbortExceptions are so frequent that it really pollutes the access logs,
drowns out 500s actually caused by the server side application, and makes monitoring and debugging
based on the access logging a lot harder.
>>
>> Fair point.
>>
>>> I'll also note that e.g. Jetty logs a 200 on ClientAbortExceptions.
>>
>> I've been looking at RFC 7231 in more detail.
>>
>> None of the status codes are ideal. Of course, they are intended for the
>> client which in this case is never going to see the status code anyway
>> but still...
>>
>> The general description of 2xx codes looks to be appropriate:
>> "... the client's request was successfully received, understood, and
>> accepted."
>>
>> 200 doesn't seem right since:
>> "...  the request has succeeded."
>>
>> 202 could be better since:
>> "... the request has been accepted for processing, but the processing
>> has not been completed."
>> but the intention behind 202 is very different so using it in this case
>> seems wrong.
>>
>> None of the other 2xx codes seem to be a match at all.
>>
>> The 4xx codes are another possibility:
>> "... 4xx (Client Error) class of status code indicates that the client
>> seems to have erred."
>>
>> Of those only 400 is a possible match.
>> "... the server cannot or will not process the request due to something
>> that is perceived to be a client error."
>>
>> The 5xx codes are also possible:
>> "... the server is aware that it has erred or is incapable of performing
>> the requested method"
>>
>> With 500 being the best match in that case:
>> "... the server encountered an unexpected condition that prevented it
>> from fulfilling the request."
>>
>> You have already explained why using 500 is a problem. 400 suffers from
>> a similar issue. Which brings us back to 200 which doesn't seem right
>> either.
>>
>> I think we are going to have to choose a "least bad" option here. Given
>> that Tomcat has used 200 in the past and that there is the option to add
>> %{javax.servlet.error.exception}r to the access log I think reverting
>> the change to the status code is the best (well, least bad) option here.
>>
>> I'll get that done shortly.
> 
> I think that it makes sense to log the status code that was actually
> sent on the first line of the response.
> 
> If "200" was sent to browser, it is better to log "200", not "500".

Note: It is possible that no status code was sent e,g, if the client
disconnected before the response was committed.

The restored behaviour is that the access log will contain whatever
status code the application set.

> 
> As an idea:
> 
> In Apache HTTPD there is an option in their access log format to log
> connection status: "%X"
> 
> http://httpd.apache.org/docs/2.4/mod/mod_log_config.html#formats
> 
> "%X":
> Connection status when response is completed:
> X = Connection aborted before the response completed.
> + = Connection may be kept alive after the response is sent.
> - = Connection will be closed after the response is sent.

That is an excellent idea. I'll add a BZ entry for that.

Mark

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